Diethanol amides of long chain monocarboxylic acids are known in the art as antistatic compounds (hereinafter "antistats") useful for incorporation into polyolefin polymers, especially polyethylene, polypropylene and/or copolymers of ethylene and propylene. One particularly demanding use for polyethylene containing such an antistat is as packaging material for packaging electronic components which comprise polycarbonate.
The commercial process for producing diethanol amide of long chain monocarboxylic acid comprises two separately conducted steps. In the first step, diethanolamine and a long chain monocarboxylic acid, alkyl ester (for example, methyl laurate), are reacted in the presence of an excess of the diethanolamine to produce a mixture comprising the diethanol amide of the long chain monocarboxylic acid and diethanolamine. Since the reaction otherwise tends to proceed only slowly, it is often conducted in the presence of a catalytic amount of a basic catalyst such as sodium methoxide which increases the reaction rate. The excess diethanolamine also serves to increase the reaction rate and to drive the reaction to substantial completion. In the case of methyl laurate, the temperature of the reaction is above the boiling point of methanol under the prevailing pressure and the reaction is customarily conducted under a slight vacuum with a nitrogen purge to sweep the methanol away substantially as it is formed. The reaction may be represented as follows: ##STR1##
Diethanolamine is not an antistat and its presence serves to dilute the antistatic properties of the composition. Most importantly, however, diethanolamine reacts with the polycarbonate of the electronic components the packaging was intended to protect.
The second step of the commercial process therefore converts the residual diethanolamine to a material less harmful to polycarbonate. Long chain monocarboxylic acid (for example, lauric acid) is added to the first reaction mixture and reacted with the residual diethanolamine to form long chain monocarboxylic acid, N,N-bis(2-hydroxyethyl)ammonium salt, which ordinarily constitutes from about 5 to about 10 percent by weight of the resulting second reaction mixture. The reaction may be represented as follows: ##STR2##
The ammonium salt is not an antistat and its presence dilutes the antistatic properties of the product composition. The product is often compounded with polyethylene at elevated temperatures, but at those temperatures the antistat composition does not have good thermal stability and a good deal of the ammonium salt degrades and forms volatile byproducts. Although the ammonium salt of fatty acids does not degrade polycarbonate as does diethanolamine, it can induce the corrosion of copper, solder, and other parts of the electronic components. Electronic components, and especially assembled circuit boards containing electronic components, are usually expensive and often must be stored for long periods of time in their packaging. The presence of more than inconsequential amounts of the ammonium salt of fatty acids renders the composition generally unfit for use in polyethylene packaging of electronic components and assembled circuit boards containing electronic components. As a matter of fact, the electronics packaging industry requires antistats that are substantially free from fatty acids and/or their salts.